Recently, a method for directly producing a strip with a thickness which is within several millimeters of the thickness of a final product, from a molten metal such as molten steel, has been studied with keen interest. When the above continuous casting method is adopted, unlike conventional continuous casting methods, it is not necessary to provide a hot rolling process including a large number of processing stages, and further it is sufficient to conduct rolling only lightly on the strip so as to obtain a final produce. Accordingly, it is possible to simplify the process and apparatus on the production line.
One of the continuous casting methods developed to accomplish the above object is a twin drum type continuous casting method disclosed in Japanese Unexamined Patent Publication (Kokai) No. 60-137562.
FIG. 1 is a perspective view to explain an outline of the above twin drum type continuous casting method. In this system, there are horizontally provided a pair of cooling drums 1a, 1b rotated in opposite directions. There is formed a recess portion between the cooling drums 1a, 1b and the side dams 2a, 2b. This recess portion is used as a molten metal pool 3 in which molten metal is accommodated. Molten metal is poured from a container such as a tundish into this molten metal pool 3 via a nozzle, and some of molten metal 4 accommodated in this molten metal pool 3 comes into contact with the cooling drums 1a, 1b and is cooled and solidified, so that a solidified shell can be formed.
This solidified shell is moved in accordance with the rotation of the cooling drums 1a, 1b. At a position where the pair of cooling drums 1a, 1b come most close to each other, that is, at a drum gap portion 6, the solidified shells respectively formed on the surfaces of the cooling drums 1a, 1b are pressed to each other, so that a target strip casting 5 can be obtained. In this case, reference numeral 15 is an end surface of the cooling drum, and reference numeral 16 is a sliding surface.
As disclosed in Japanese Unexamined Utility Model Publication (Kokai) No. 63-90548, each side dam 2a, 2b of this continuous sheet bar casting apparatus includes: a heat insulator accommodated in the side dam case; a base member attached to the heat insulator; and a ceramic plate attached to a portion of the base member corresponding to the cooling drum. Due to the foregoing arrangement, the side dam is pushed against the end surface of the cooling drum at the time of casting, and the ceramic plate is worn away when it comes into contact with the end surface of the cooling drum, so that a gap between the ceramic plate and the end surface of the cooling drum can be eliminated. Therefore, it is possible to prevent a leakage of molten steel. As disclosed in Japanese Unexamined Patent Publication (Kokai) No. 61-266160, in general, the side dam is oscillated, so that the abrasion of the ceramic plate can be accelerated.
In the above continuous strip casting apparatus, an amount of steel to be cast is determined by an abrasion speed of the ceramic plate of the side dam which slides on the end surface of the cooling drum. Therefore, it is very important to suppress the abrasion of the ceramic plate in order to increase an amount of steel to be cast.
The abrasion of the ceramic plate is affected by the factors such as its hardness, surface temperature and surface roughness. In order to suppress the abrasion of the ceramic plate, lubricant is fed onto the abrasion surface of the ceramic plate slidably coming into contact with the end surface of the cooling drum. Due to the foregoing, the abrasion can be reduced by the function of the lubricant, and further the surface temperature of the ceramic plate can be lowered and the end surface of the cooling drum can be made smooth. Accordingly, it is possible to reduce a coefficient of friction between the sliding surface of the cooling drum and the abrasion surface of the ceramic plate. As a result, it is possible to prevent the side dam from being opened. Therefore, the sealing property can be improved so as to prevent a leakage of molten steel.
Concerning the means for feeding lubricant onto the abrasion surface of the ceramic plate, Japanese Unexamined Patent Publication (Kokai) No. b 63-248547 discloses a method in which solid lubricant is pushed against the end surface of the cooling drum or the abrasion surface of the ceramic plate of the side dam by the operation of an air cylinder, or alternatively fine powder of solid lubricant dispersed in liquid is sprayed and made to adhere onto the end surface of the cooling drum or the abrasion surface of the ceramic plate of the side dam.
However, when a ordinary side dam is used and solid lubricant is simply made to adhere onto the sliding surface as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 63-248547, a sufficient lubricating effect cannot necessarily be obtained at the sliding surface. That is, when an amount of lubricant that has adhered onto the end surface of the cooling drum is small, or even if the amount of lubricant is sufficiently large, when lubricant is scratched off by an inlet portion 11, which is indicated by an arrow in FIG. 2(a) and located on the inlet side in the rotational direction of the drum, of the side end ceramic plate coming into contact with the end surface of the cooling drum, it is impossible to obtain a sufficiently great lubricating effect. On the other hand, when an amount of solid lubricant that has adhered onto the end surface of the cooling drum is too great, lubricant that has exuded out from a gap between the end surface of the cooling drum and the sliding surface of the side end ceramic plate gets into the molten steel pool. Therefore, the molten steel is contaminated. When a gap between the end surface of the cooling drum and the side end ceramic plate is extended so as to prevent the above problem, molten steel tends to be inserted.